The invention relates to a projection exposure device, in particular for micro-lithography, to produce an image of an object in an image plane positioned in an object plane with a radiation source emitting projection radiation, with illumination optics positioned in the ray path between the light source and the object plane and projection optics positioned in the ray path between the object plane and the image plane, whereby a filter with a moveable filter element is placed in a filter plane, which lies in the vicinity of a pupil plane between the light source and the object plane, which is moveable in the filter plane and has a distribution of the transmission factor over the filter face in such a way that the intensity distribution of the projection light perpendicular to the optical axis in the ray path after the filter, changes with the movement of the filter element.
Such a projection exposure device is known from U.S. Pat. No. 5,264,898. The filter used there has filter elements which completely block the projection light in certain areas and allow it to pass through in other areas. The filter is intended to be used to optimise the focal length of the illumination optics in the object plane while preserving the resolution of the projection exposure device.
Especially in projection operations, where three dimensional structures are projected, thus for example when transferring three dimensional structures from a recticle to a wafer in connection with micro-lithography, it has been shown that it is a matter not only of homogeneous as possible illumination of the object plane but also of well-defined distribution of the illumination angle in the object plane, i.e the angles under which the projection radiation strikes the object plane. The illumination angle distribution to be set depends on how the structures are positioned on the recticle and what extension they have perpendicular to the object plane. For different recticle structures therefore different illumination angle distributions may have to be preset for optimum projection.
If the filter in U.S. Pat. No. 5,264,898 (which has a completely different purpose, as explained above), were to be used for the defined presetting of illumination angles, there would be no possibility in addition of influencing the illumination angle distribution.
The present invention introduces further developments of a projection exposure device of the type mentioned above to enable a pre-set illumination angle distribution to be set accurately.
Accordinly, the invention provides a projectino exposure device which includes a filter element having a transmission factor, at least in certain areas for the projection light, which is greater than zero and less than 100%.
With a filter having such a filter element in the filter plane with the degree of freedom of movement, for example a translation or rotation of the filter element, and at least in certain areas partial permeability, two degrees of freedom are now available to produce the desired illumination angle distribution in the object plane with the aid of the filter from a given projection light distribution by setting the corresponding transmission in the vicinity of a pupil plane in front of the object plane. A change of the object structure to be projected or alterations in the illumination, which occur during the operation of the projection exposure device, can be compensated by re-adjusting the moveable filter element. Alternatively or in addition with the moveable filter element, illumination settings already preset elsewhere, therefore the illumination angle, for example pre-set by a corresponding aperture shutter, can be finely adjusted.
The transmission factor of the filter element can be non rotation-symmetrical over the filter face in regard to the optical axis of the projection optics and the filter element can be retained in such a way that it can be turned around the optical axis. With a filter, which has such a filter element, by turning the filter element when replacing the recticle the illumination angle distribution can be adapted to the type of recticle used, therefore the object structure to be projected. In addition changes in the illumination can be corrected which finish up in a rotation of a distribution of the illumination intensity in the pupil plane which is non rotation-symmetrical to the optical axis. The filter element rotatable around the optical axis is reset according to the rotation of this intensity distribution so that the intensity distribution after the filter corresponding to a preset distribution which equates to an illumination angle distribution, remains unchanged. Such changes of the illumination intensity distribution in the pupil plane can for example result from time drifts of the properties of the light source or the optical properties of the illumination optics. Also adjustment of the light source or the illumination optics or a change of the illumination setting can cause such a rotation of the illumination intensity distribution.
The filter can have at least one filter element with transmission factor varying in the axial direction to the optical axis. This results in the possibility with the filter to influence areas, with varying distance to the optical axis in a variety of ways. Therefore more complex illumination angle distributions can also be set or reset.
The filter can be a continuously graduated filter. With such filters with at least one filter element with a constantly changing transmission factor, corresponding constant illumination angle distributions can be produced.
Alternatively the filter element can have at least two zones with a varying transmission factor. At the zone borders here it can be a matter of step-shaped progression of the transmission factor. Within the zones the transmission can be constant or again a continuous progression. Such subdivision into zones facilitates defined presetting or defined resetting of an illumination angle distribution.
Preferably the free aperture of the illumination optics in the filter plane is circular and the filter has at least one filter element with multiple zones with a transmission factor varying in the circumferential direction. With such filter elements for example an illumination angle distribution with multiple symmetry can be set.
The filter element can have at least two zones with a transmission factor varying in the radial direction. Also here subdivision into zones facilitates defined presetting or defined resetting of an illumination angle distribution. If subdivision takes place in zones both in the circumferential direction as well as in the radial direction, the freedom when setting an illumination angle distribution is particularly great.
The filter element can have four quadrants with transmission factor alternating in the circumferential direction. With such a filter element an illumination angle distribution which has dual symmetry, i.e. so-called ellipticity, can be adjusted with pre-set orientation of the ellipse. Alternatively or in addition such a filter element can be used to compensate already existing ellipticities. Such ellipticities can for example arise due to the geometry of the light source or the illumination optics or even due to an illumination setting already preset elsewhere.
Preferably the filter has at least two filter elements which are retained in such a way that they can be turned in relation to each other. The distribution of the total transmission factor arising as a result on two filter elements again increases the freedom of presettable or resettable illumination angle distributions.
Here a rotation-symmetrical transmission factor of the filter can result with a relative position of the filter elements. Therefore there is a position of the moveable filter element, in which the filter, at least concerning its influence on the rotation-symmetry, acts neutrally.
In a simple way the rotation-symmetrical properties of the illumination angle distribution can thus be tested or used with no filter influence when the filter is fitted. Especially the filter elements can be designed so that the transmission factor in a relative position of the filter elements is constant over the whole filter face; so that the filter influence on the illumination angle distribution, e.g. for test purposes, can be totally eliminated.
Preferably a drive mechanism coupled with the rotatable filter element is provided. This allows automated presetting or resetting of an illumination angle distribution.
In the case of a preferred embodiment form, a control device acting together with the drive mechanism is provided which, depending on a preset illumination angle distribution of the projection light in the object plane, triggers the drive mechanism to engage a pre-set position of the filter element. Thus for example depending on available information the light source or the illumination optics of the filter can be automatically set or reset via the recticle structure or the actual setting.
At least one detector device acting together with the control device to record the intensity distribution of the projection light can be provided in a plane perpendicular to the optical axis. This allows the illumination angle distribution to be tracked by correspondingly following the moveable filter element depending on the intensity distribution detected.
The detector device can have a two-dimensional CCD array. Such a detector device has a high position resolution and is light-sensitive.
The detector device can be designed so that it calculates the illumination angle distribution of the projection light in the object plane. The directly measured illumination angle distribution is the ideal input quantity for re-adjustment with the aid of the moveable filter element.